1. Field of the Invention
The present invention relates to an ink jet recording apparatus and a method for controlling the ink jet recording apparatus.
2. Related Background Art
The serial type printer represented by the ink jet recording apparatus (printer) performs printing with the recording head that scans in the direction orthogonal to the conveying direction of a recording medium, and conveys the recording medium in a portion corresponding to the width of the recording head when one-time scanning is completed. A recording is executed by the repetition of such printing operation and conveyance of the recording medium. Inside the printer, then, the recording data, which have been transmitted from a host, are developed (stored) on a print buffer, and the data thus developed are converted so as to match them with the nozzle array of the recording head. The data that correspond to the nozzle length of the recording head are transferred one after another, thus discharging ink from the nozzles of the recording head that moves for the formation of images.
At this juncture, the xe2x80x9cnull skip controlxe2x80x9d is executed for the purpose of improving the speed of process and reducing the volume of print buffer storage. This is an operation such that when the recording data in the scanning direction of the recording head are zero (null) and in the zero status (null condition), which is made to continue for a specific unit in the conveying direction of a recording medium, the data are not developed (written) on the print buffer. Instead, null flags are set corresponding to the zero data.
(i) in FIG. 3 is a view that shows the state of the recording data stored on the print buffer without using the null skip control. Here, (i) in FIG. 3, the direction X is the scanning direction of the recording head, and the direction Y is the conveying direction of a recording medium. In the areas (5), (6), (11), and (12) of (i) in FIG. 3, all the recording data are null in the scanning direction of the recording head described earlier, and the null status continues for a specific unit (an eight-nozzle portion, for instance) in the conveying direction of the recording medium. In a case where the null skip control is not executed like this, null data are stored on the print buffer corresponding to such areas.
(iii) in FIG. 3 is a view that shows the storing state of the recording data on the print buffer as in the case illustrated at (i) in FIG. 3, but by use of the null skip control.
There is provided a null flag table that indicates whether or not the null data occupy each area per a specific unit in the conveying direction of the recording medium. The null skip control is executed with reference to information on this null flag table. The null flags corresponding to the areas (5), (6), (11), and (12) described earlier are set (the value thereof is set at 1), thus saving the development of null data on the print buffer. Then, as the reading process of the print buffer where the null flags are set, each dummy reading is performed on the next address of the print buffer where the null flag is set. Then, the null data is transferred to the recording head instead of the data thus read.
Also, when recording data are written (being written) into the print buffer or read out (being read out) from the print buffer, DMA means is used. Here, for a printer, a plurality of DMA means (DMA channels) is provided. When this means is used, the DMA bus is occupied in accordance with the order of priority. There are known such methods as the one that uses it in accordance with the predetermined order (priority order method) and the one that monitors the DMA channel one after another (cyclic method).
Besides the writing process and reading process of the print buffer described above, DMA means uses the DMA functions with respect to the request from the CPU for bus occupation, the recording data processing, the refreshing operation of a DRAM, the motor control, and the communications with the host, among some others.
As a result, while DMA means occupies the DMA bus for the execution of writing or reading process for the print buffer, the execution of other DMA processes (requests for the DMA) is required to wait eventually until the DMA bus is released.
For the execution of this null skip control, it has been practiced for DMA means to perform reading process of the reading data on the print buffer under any circumstances, irrespective of the presence or absence of null data on the print buffer having the null flag set thereon. In this case, if the null flag is set, the data thus read out is transferred to the recording head after having been converted into null data.
Also, when the null skip control is executed, it has been practiced for DMA means to perform reading process of the recoding data on the print buffer under any circumstances, irrespective of the presence or absence of null data on the print buffer having the null flag set thereon. In this case, if the null flag is set, the data thus read out is transferred to the recording head after having been converted into null data.
As a result, the occupation rate of the DMA bus increases, and there is encountered a problem that it takes a time to execute the process of DMA transfer, because the bus is not released despite the DMA request has been issued.
The present invention is designed with a view to solving the problems discussed above. It is an object of the invention to provide an ink jet recording apparatus and a method for controlling such ink jet recording apparatus serving the purpose.
In order to achieve the aforesaid object, the ink jet recording apparatus of the present invention, which is provided with plural print buffers for storing recording data, and a null flag table capable of setting a null flag corresponding to the print buffers instead of storing null data on the print buffers, comprises data converting means for converting specific data, being provided with plural writable blocks for writing the recording data, and a counter for retaining a value to designate the writable blocks; clear means for zero clearing the writable blocks in accordance with the values of the counter; DMA means for reading out the recording data from the print buffers for writing the recording data on the writable blocks; and control means for enabling the clear means to zero clear the writable blocks when the null flag is set on the null flag table corresponding to the print buffers, instead of the performance of process by the DMA means to read out data from the print buffers.
A method of the present invention for controlling an ink jet recording apparatus, which is provided with plural print buffers for storing recording data, a null flag table capable of setting a null flag corresponding to the print buffers, and data converting means for performing specific conversion of the recording data written on a writable block, comprises the steps of reading out the recording data from the print buffers by DMA means; zero clearing the writable block by clear means; and executing the clearing step instead of executing the reading out step corresponding to the null flag when the null flag is set on the null flag table corresponding to the print buffers.
Also, the ink jet recording apparatus of the present invention, which is provided with plural print buffers for retaining recording data for recording by enabling a recording head to scan on a recording medium, and a null flag table capable of setting null flags corresponding to specific number of data instead of storing null data on the print buffers, comprises DMA means for reading out the recording data from specific number of print buffers per scan; null flag examination means for examining the null flags corresponding to each of the specific number of print buffers; and control means for enabling the null flag examination means to examine the null flags per scan for the suspension of reading of the DMA means when all the null flags are found to be set as the result of the examination.
Also, the method of the present invention for controlling an ink jet recording apparatus, which is provided with plural print buffers for retaining recording data for recording by enabling a recording head to scan on a recording medium, and a null flag table capable of setting null flags corresponding to specific number of data instead of storing null data on the print buffers, comprises the steps of reading out the recording data from specific number of print buffers per scan by DMA means; examining null flags on the null flag table corresponding to each of the specific number of print buffers; and suspending the reading when the null flags are all set.